To that statement I'd immediately ask, "what did we do before there were smartphones? Did we not investigate crimes? Can't we do that now?"

Criminals have always tried to hide their activities and keep secrets. Sure with strong encryption maybe some information is hard to search, but that was always the case. (Did they ever find Jimmy Hoffa's body?)

I mostly agree with the idea that we have a lot more to lose by inserting backdoors than we would ever gain.